Certain industrial processes such as electroplating generate waste waters containing high concentration of chromate. Also, waste solutions from the production of sodium chromate from chromite ore contain high chromate concentrations. Chromate is very toxic, and there is convincing evidence that it is both mutagenic and carcinogenic. It is, therefore, important that chromate be removed from contaminated water before that water is returned to the environment.
Chromate can be removed from solution by the use of a chemical reducing agent. Such agents reduce the chromium from Cr.sup.+6 to Cr.sup.+3, in which form it can be precipitated. Other methods of chromate removal involve dialysis of chromate-bearing wastes and the use of ion-exchange methods. These latter approaches do not require chromate reduction.
Disclosure of the capability of Pseudomonas dechromaticans to biochemically reduce chromates and bichromates only under anaerobic conditions is found in U.S. Pat. No. 3,941,691--Romanenko et al. This same work has also been reported in the literature, "A Pure Culture of Bacteria Utilizing Chromates and Bichromates As Hydrogen Acceptors in Growth Under Anaerobic Conditions" by Romanenko and Korenkov [Mikrobiologiya 46, pp. 414-17 (1977)]. In addition, it has been reported by Lebedeva and Lyalikova in "Reduction of Crocoite by Pseudomonas chromatophila sp. nov." [Mikrobiologiya 48, pp. 517-22 (1979)] that the chromium in the mineral crocoite (PbCrO.sub.4) can be reduced only under anaerobic conditions to Cr.sup.+3 by Pseudomonas chromatophila.
Chromate is very toxic to normal microorganisms, most of which cannot tolerate concentrations of K.sub.2 CrO.sub.4 higher than 10-20 ppm in minimal salts media. Included among the microorganisms sensitive to chromate are those microorganisms necessary for the digestion of sewage. Therefore, the introduction of waste water containing elevated chromate levels into sewage digesters poses an additional problem over and above the health problems engendered by the release of chromate to the environment.